Various types of vertical axis wind turbine (VAWT) rotors have been proposed in the past for use with a wide variety of devices, including pumps, propellers, and for generating electricity. The Savonius VAWT has been known since the 1920s, but has not yet been widely implemented commercially. Also, there is a general feeling in the art that it is unsuitable for commercial generation of electricity.
A conventional drawback of the Savonius VAWT is often considered to be its cumbersome construction, which includes two or more structural end caps. Typically, a plurality of vanes (normally two in practice) are mounted between two end caps, or if more than one stage is provided, then one or more intermediate “end” caps are provided. The end caps often provide the major structural support for the vanes, and are connected to a shaft for rotation about a vertical axis [see, for example, Sigrud Savonius' U.S. Pat. No. 1,697,574 and British Patent 244,414].
In U.S. Pat. No. 4,830,570 a version of a Savonius VAWT is provided which in addition to end caps, uses a structural support system for indirectly connecting the vanes (the patentee calls them “blades”) to a central shaft. At spaced locations along the shaft the patentee provides structural members extending radially from a sleeve which surrounds and is rigidly attached to the shaft. At those locations ribs are connected to the vanes and extensions of those ribs are connected to the radial structure members. Also further diagonal structural members connect the ribs to the radial structural members, providing a complex arrangement that appears to be very difficult to construct, and undesirably expensive. While the patentee suggests that for very small rotors a much simpler design would work, how the design would be simpler is not described.
According to the invention, a Savonius VAWT rotor is provided that undoubtedly performs at least as well as the rotor in the '570 patent yet is much, much simpler, eliminating components apparently considered necessary in the '570 patent without elimination of their function. According to the invention, a Savonius VAWT is provided wherein vane support hubs are provided with curved spokes extending radially outwardly therefrom and preferably integral therewith (e.g. formed of the same piece of metal). The hub directly engages and is operatively connected to the shaft. No structural end caps, separate radial structural supports, or diagonal structural supports, as are utilized in the '570 patent arrangement, are necessary, yet the rotor maintains structural integrity and functions well even in high winds. The hubs may also be operatively attached to the shaft by removable fasteners, for quick assembly of the rotor, and to allow disassembly for repair or reconstruction if necessary.
According to one aspect of the invention there is provided a Savonius vertical axis wind turbine rotor comprising: A shaft, substantially vertical in use. A plurality of vane support hubs each having a plurality of at least partially curved spokes extending substantially radially outwardly therefrom. The vane support hubs are operatively connected directly to the shaft and spaced vertically from each other along the shaft to provide a plurality of sets of vertically spaced spokes. And a plurality of vanes, one for each set of spokes, operatively connected to the spokes to provide surface area for engaging wind (which causes the shaft to rotate during use, when mounted in bearings). Providing the construction according to the invention, the rotor is devoid of structural end caps, greatly simplifying the construction, improving appearance, and reducing the weight of the structure significantly (all other things being equal).
In one form of the invention, each vane support hub has exactly three spokes. It has been found that three spokes (and thus three vanes) are desirable for many purposes despite prior art teachings indicating that three vanes are much less desirable. [E. g. see column 9, lines 38+ of the '570 patent, the cancellation of the three vane version from the Savonius British patent, and the 1977 finding in the Sandia Laboratories report “Wind Tunnel Performance Data for Two- and Three-Bucket Savonius Rotors” SAND76-0131 at page 31 that “The maximum power coefficient of the two-bucket configuration is approximately 1.5 times that for the three-bucket configuration”.]
Preferably, the vane support hubs are operatively connected to the shaft using mechanical fasteners, such as removable fasteners. Also, the vanes may be connected to the spokes using mechanical fasteners. The mechanical fasteners may directly connect the vane support hubs to the shaft.
It is desirable that at least four vane support hubs are provided vertically spaced along the shaft, with the spoke sets thereof substantially vertically aligned with each other. The vane support hubs and spokes are preferably integral and made of metal (e.g. aluminum or titanium) or fiber (e.g. carbon fiber) reinforced plastic. The vanes may be made of sheet metal, or high performance sail cloth.
The Savonius VAWT rotor may be provided in combination with at least one bearing assembly mounting the shaft substantially vertically for rotation about a substantially vertical axis, and a propeller, electricity generating device, or pump operatively connected to the shaft to be powered thereby.
According to another aspect of the invention, a vane support assembly for a Savonius or open helix vertical axis wind turbine is provided comprising: A vane support hub defining a substantially central through-extending opening therein. A plurality of at least partially curved spokes integral with the vane support hub and extending substantially radially outwardly therefrom; and an adaptation part of the hub which allows the hub to be operatively connected to a substantially vertical shaft extending through the through-extending opening, for rotation with the shaft. The adaptation may be an opening in a part of the hub, such as a radial opening in the hub which extends to the through-extending central opening and is adapted to receive a mechanical fastener, keying on the hub, or a variety of other structures. As with the rotor, the vane support hub per se may include exactly three integral spokes, and the vane support hub and integral spokes may be made of metal or fiber reinforced plastic.
According to another aspect of the invention there is provided a Savonius or open helix VAWT comprising: At least one bearing. A substantially vertical shaft mounted by the at least one bearing for rotation about a substantially vertical axis. At least four vane support hubs each having a plurality of at least partially curved spokes extending substantially radially outwardly therefrom. The vane support hubs are operatively connected (e.g. directly) to the shaft and spaced vertically from each other along the shaft to provide a plurality of sets of vertically spaced spokes. The turbine is devoid of structural end caps. A plurality of vanes, one for each set of spokes operatively connected to the at least partially curved spokes to provide surface area for engaging wind; and a propeller, electricity generating device, or pump operatively connected to the shaft to be powered thereby. As with the rotor, if desired three spokes are provided for each vane support hub, and the spokes and hub may be integral.
The presently claimed features of the invention, or aspects thereof, are mostly clearly seen in FIGS. 31-37, 45 & 46 of the appended drawings (and are described in the text associated therewith).
It is the primary object of the invention to provide a desirable construction of a VAWT, rotor therefor, and vane support assembly therefor. This and other objects of the invention will become clear from a detailed inspection of the invention, and from the appended claims.